1. Field of the Invention
The present invention relates to a manufacturing method for and to an apparatus for manufacturing high-quality coated optical fibers at high speed, and to coated optical fibers whose coating layers have superior surface smoothness.
2. Description of Related Art
Conventionally, coated optical fibers are manufactured by employing the following method. In the first process, an optical fiber preform (i.e., base material) is melted at approximately 2,000xc2x0 C. so as to form a bare optical fiber by drawing. The bare optical fiber is then made to pass through a cooling system so that the temperature of the bare optical fiber is decreased to approximately 100xc2x0 C. or lower. The bare optical fiber is then coated with a UV curable resin or a thermosetting resin by using a resin coating system, and the resin is cured by using a resin curing system, thereby yielding a coated optical fiber. This coated optical fiber is wound up by a take-up via pulleys.
Recently, productivity has been improved by employing high-speed drawing. However, at high drawing speed of 400 m/min or higher, the amount of movement of the optical fiber in the lateral direction (i.e., perpendicular to the fiber-running direction) increases. In this case, (i) the optical fiber may contact the nipple of the resin coating system, which degrades the strength of the optical fiber, or (ii) the thickness of the coating layer is not uniform, which degrades the characteristics with respect to the lateral (or side) pressure. Here, increase of the flow rates of (i) the gas for cooling the bare or coated optical fiber and (ii) the purge gas in the resin curing system is a cause of such increase of movement of the optical fiber, because the optical fiber vibrates due to the flow of the above gases. There may be various other causes, but the inventors of the present invention found that the smoothness of the surface of the pulley, which the coated optical fiber first contacts, is also related to such movement of the optical fiber in the lateral direction.
In order to solve the above problem, Japanese Patent No. 2863071 discloses a process of manufacturing a coated optical fiber by forming a coated layer around a bare optical fiber and winding this fiber using solid bodies such as pulleys by a winding system, where the surface roughness of the solid body which the coated optical fiber first contacts is 0.6 xcexcm or less. The objective of this invention is to reduce (i) the movement of the optical fiber in the lateral direction and (ii) unevenness of the thickness of the coating layer, and the usage of a solid body having a smooth surface suppresses the lateral movement or vibration of the optical fiber due to the unevenness of the surface of the solid body.
However, though the above conventional invention has the objective of reducing the lateral movement of the optical fiber and the unevenness of the thickness of the coating layer, the conventional invention has no objective of improving the smoothness of the surface of the coated optical fiber. In addition, Japanese Patent No. 2863071 discloses only the surface roughness of the solid body which the coated optical fiber first contacts and does not disclose the surface roughness of each of the following solid bodies which, the optical fiber contacts in turn and of the solid bodies used in the processes other than the drawing process, for example, solid bodies which the optical fiber contacts in a rewinding process.
In addition, the surface temperature and the Young""s modulus of the optical fiber are not investigated in the above patent.
In the drawing process of the coated optical fiber, the temperature of the coating layer of the coated optical fiber after passing through the UV lamp (i.e., UV radiation device) is higher than room temperature, and such a high-temperature coated optical fiber contacts solid bodies such as a capstan (to which the fiber is applied) and a dancer (including a dancer pulley) before being wound up by the take-up (i.e., winding system or machine).
Generally, the capstan, the dancer, a path line pulley, and the take-up are made of metal. For example, iron (Fe) has a Young""s modulus of 60,000 MPa (megapascal) though this value varies due to the quality of the material. Stainless steel and aluminium have Young""s moduli of a similar order. Other materials such as ceramics may also be used; however, these materials are all hard material and have a Young""s modulus of a few ten thousand MPa.
On the other hand, the surface of the outer coating layer of the coated optical fiber has a Young""s modulus of approximately a few hundred MPa, and as explained above, the Young""s modulus of each solid body, which the optical fiber contacts, is a few ten thousand MPa. It is obvious that when a hard body is pushed against a softer material (i.e., the coating layer of the coated optical fiber), the softer coating layer will deform. In particular, if the temperature of the outer coating layer of the coated optical fiber is high, such contact with a solid body causes considerable effects on the coating layer.
Therefore, when the surface smoothness of the solid bodies, which the coated optical fiber contacts, is inferior, the surface of the coated optical fiber is made slightly uneven. Such an uneven surface may be easily observed as being an inferior product, thereby considerably degrading its commercial value.
In addition the coated optical fiber is generally coated with a colored ink so as to distinguish each fiber from the others when coated optical fibers are coated so as to produce an optical cable, cord, ribbon, or tape. If the surface of the optical fiber is slightly uneven, the performance of the colored ink coating may be degraded.
In consideration of the above circumstances, an object of the present invention is to investigate the relationships between the temperature and the Young""s modulus of the outer coating layer of the optical fiber and the surface roughness of the solid bodies which contact the optical fiber during the drawing process, and to provide a manufacturing method and apparatus for manufacturing a coated optical fiber which has a superior surface smoothness of a resin coating and which can be coated with a colored ink with high coating performance, thereby preventing inferiority of the appearance and coloring on the coated optical fiber which is caused by inferior smoothness of the surface of the resin coating layer.
Therefore, the present invention provides a method of manufacturing a coated optical fiber, comprising the steps of:
making a coated optical fiber by forming an outer coating layer around a bare optical fiber; and
winding the coated optical fiber via pulleys by a take-up,
wherein the surface roughness of each solid body which the outer layer of the running coated optical fiber contacts is 0.8 xcexcm or less.
According to the above method, the smoothness of the outer coating layer of the coated optical fiber can be improved. Therefore, it is possible to manufacture a coated optical fiber having superior surface smoothness and superior coloring performance using a colored ink.
As a typical example, when the temperature of the outer coating layer is 35xc2x0 C. or higher, the surface roughness of each solid body which the outer layer of the coated optical fiber contacts is 0.8 xcexcm or less.
As another typical example, when the Young""s modulus of the outer coating layer is 500 MPa or lower, the surface roughness of each solid body which the outer layer of the coated optical fiber contacts is 0.8 xcexcm or less.
The present invention also provides a method of manufacturing a coated optical fiber, comprising the steps of:
making a coated optical fiber by forming an outer coating layer around a bare optical fiber; and
winding the coated optical fiber via pulleys by a take-up,
wherein when at least one of the conditions that the temperature of the outer coating layer is a room temperature and the Young""s modulus of the outer coating layer is higher than 500 MPa is satisfied, the surface roughness of each solid body, which the outer layer of the coated optical fiber contacts during drawing or rewinding, is 1.2 xcexcm or less.
Accordingly, the smoothness and the coloring performance (using a colored ink) of the outer coating layer of the coated optical fiber can be improved while the manufacturing cost is reduced.
The present invention also provides a coated optical fiber manufactured by a method as explained above, wherein the coated optical fiber has an average surface roughness of 0.2 xcexcm or less (0.15 xcexcm or less is more preferable) so as to reduce the defect percentage of coloring of the fiber.
The present invention also provides an apparatus for manufacturing a coated optical fiber, comprising:
a drawing furnace for melting an optical fiber preform and forming a bare optical fiber;
a cooling system for cooling the formed bare optical fiber;
a resin coating system for coating the bare optical fiber with resin which functions as an outer coating layer of the coated optical fiber;
a curing system for curing the resin; and
pulleys arranged in a path line along which the coated optical fiber is transferred to a take-up,
wherein the surface roughness of each solid body which the outer layer of the running coated optical fiber contacts is 0.8 xcexcm or less.
According to the above apparatus, the smoothness of the outer coating layer of the coated optical fiber can be improved. Therefore, it is possible to manufacture a coated optical fiber having superior surface smoothness and superior coloring performance using a colored ink.
The present invention also provides an apparatus for manufacturing a coated optical fiber, comprising:
a drawing furnace for melting an optical fiber preform and forming a bare optical fiber;
a cooling system for cooling the formed bare optical fiber;
a resin coating system for coating the bare optical fiber with resin which functions as an outer coating layer of the coated optical fiber;
a curing system for curing the resin; and
pulleys arranged in a path line along which the coated optical fiber is transferred to a take-up,
wherein when at least one of the conditions that the temperature of the outer coating layer is a room temperature and the Young""s modulus of the outer coating layer is higher than 500 MPa is satisfied, the surface roughness of each solid body (i.e., a constituent of the path line) which the outer layer of the coated optical fiber contacts is 1.2 xcexcm or less.
Accordingly, the smoothness and the coloring performance (using a colored ink) of the outer coating layer of the coated optical fiber can be improved while the manufacturing cost is reduced.
The present invention also provides a coated optical fiber manufactured by an apparatus as explained above, wherein the coated optical fiber has an average surface roughness of 0.2 xcexcm or less (0.15 xcexcm or less is more preferable) so as to reduce the defect percentage of coloring of the fiber.